Reductions of M{N(SiMe3)2}3 (M = V, Cr, Fe): Terminal and Bridging Low-Valent First-Row Transition Metal Hydrido Complexes and “Metallo-Transamination”

The reaction of the vanadium­(III) tris­(silylamide) V­{N­(SiMe3)2}3 with LiAlH4 in diethyl ether gives the highly unstable mixed-metal polyhydride [V­(μ2-H)6[Al­{N­(SiMe3)2}2]3]­[Li­(OEt2)3] (1), which was structurally characterized. Alternatively, performing the same reaction in the presence of 12-crown-4 affords a rare example of a structurally verified vanadium terminal hydride complex, [VH­{N­(SiMe3)2}3]­[Li­(12-crown-4)2] (2). The corresponding deuteride 2D was also prepared using LiAlD4. In contrast, no hydride complexes were isolated by reaction of M­{N­(SiMe3)2}3 (M = Cr, Fe) with LiAlH4 and 12-crown-4. Instead, these reactions afforded the anionic metal­(II) complexes [M­{N­(SiMe3)2}3]­[Li­(12-crown-4)2] (3, M = Cr; 4, M = Fe). The reaction of the iron­(III) tris­(silylamide) Fe­{N­(SiMe3)2}3 with lithium aluminum hydride without a crown ether gives the “hydrido inverse crown” complex [Fe­(μ2-H)­{N­(SiMe3)2}2(μ2-Li)]2 (5), while treatment of the same trisamide with alane trimethylamine complex gives the iron­(II) polyhydride complex Fe­(μ2-H)6[Al­{N­(SiMe3)2}2]2[Al­{N­(SiMe3)2}­(NMe3)] (6). Complexes 2–6 were characterized by X-ray crystallography, as well as by infrared, electronic, and 1H and 13C (complex 6) NMR spectroscopies. Complexes 1 and 6 are apparently formed by an unusual “metallo-transamination” process.